2. PN Junctions, Diodes and Applications

Introduction and Context

The p–n junction is the basic physical structure from which a large family of semiconductor devices is formed. Although a diode contains only one junction, its behavior introduces several ideas that recur throughout electronics: carrier diffusion, electric fields, depletion regions, bias-dependent conduction, breakdown, temperature dependence, and nonlinear circuit modeling. Rectifiers, signal detectors, clippers, clampers, voltage multipliers, light-emitting diodes, photodiodes, and many protection circuits are all practical expressions of junction-device physics.

An ideal diode is often represented as a one-way switch. This representation is useful for first-order reasoning, but engineering design requires more accurate models. A real diode has a finite forward voltage, dynamic resistance, reverse leakage, junction capacitance, charge-storage effects, temperature dependence, power dissipation, and a limited reverse-voltage capability. The central task is therefore to select a model whose accuracy is appropriate to the circuit and then verify the design against electrical, thermal, and reliability constraints.

This chapter develops the junction theory needed to derive diode behavior and then applies it to common circuits. Particular attention is given to rectifier performance, waveform-shaping networks, voltage multipliers, Zener regulation, and the non-idealities that distinguish practical circuits from idealized diagrams.

Learning Objectives

After studying this chapter, the reader should be able to:

1. Explain the formation of a p–n junction, depletion region, built-in potential, and junction electric field.

2. Derive and interpret the diode current–voltage relationship.

3. Select piecewise-linear, constant-voltage, small-signal, and exponential diode models.

4. Analyze half-wave, full-wave, bridge, capacitor-input, and regulated rectifiers.

5. Design and distinguish clippers, clampers, voltage multipliers, and detector circuits.

6. Explain Zener and avalanche breakdown and design a practical shunt regulator.

7. Account for temperature, reverse recovery, leakage, capacitance, power, and tolerances.

8. Evaluate diode circuits using engineering trade-offs rather than ideal assumptions alone.

Formation and Physics of the p–n Junction

A pure semiconductor contains equal concentrations of electrons and holes at thermal equilibrium. Doping introduces donor atoms, producing n-type material with electrons as majority carriers, or acceptor atoms, producing p-type material with holes as majority carriers. When p-type and n-type regions are joined, electrons diffuse from the n side toward the p side, while holes diffuse in the opposite direction. Near the interface these carriers recombine, leaving behind fixed ionized donors and acceptors.

The region depleted of mobile carriers is called the depletion region or space-charge region. The uncovered positive donor ions on the n side and negative acceptor ions on the p side establish an electric field directed from n to p. This field opposes further majority-carrier diffusion. At thermal equilibrium, the diffusion tendency and electric-field-driven drift exactly balance, so the net current is zero.

For an abrupt junction, the depletion width is approximately

W = sqrt[(2 epsilon_s/q)(1/N_A + 1/N_D)(V_bi - V_A)]

where epsilon_s is semiconductor permittivity, q is electronic charge, N_A and N_D are acceptor and donor concentrations, V_bi is the built-in potential, and V_A is the applied voltage under a sign convention in which forward bias reduces the barrier. Under reverse bias, the effective barrier increases and the depletion region widens. Under forward bias, it narrows.

The built-in potential is related to doping and intrinsic carrier concentration by

V_bi = (kT/q) ln(N_A N_D/n_i^2).

This potential is not a voltage that can be measured directly across isolated terminals at equilibrium, because contact potentials elsewhere in the complete structure compensate it. It is nevertheless essential in explaining the internal electric field and depletion width.

Forward and Reverse Bias

Forward bias connects the p side to a higher potential than the n side. The potential barrier is reduced, allowing majority carriers to cross the junction. Once injected into the opposite region, they become minority carriers and diffuse away from the junction. The resulting current increases approximately exponentially with applied voltage.

Reverse bias raises the barrier and widens the depletion region. Only a small reverse saturation current flows, primarily due to thermally generated minority carriers. If the reverse voltage becomes sufficiently large, breakdown occurs. Breakdown is not automatically destructive; a properly current-limited Zener diode is deliberately operated in this region. An ordinary rectifier diode, however, may be damaged if its reverse-voltage and power ratings are exceeded.

The Diode Equation and Practical Models

For an idealized junction under conditions where recombination, generation, and series resistance are represented adequately by a single empirical parameter, the current is

I_D = I_S [exp(V_D/(nV_T)) - 1],

where I_S is the reverse saturation current, n is the ideality factor, and V_T = kT/q is the thermal voltage. At 300 K, V_T is approximately 25.85 mV. The ideality factor is commonly near 1 when diffusion dominates and near 2 when recombination in the depletion region is important.

The equation explains why a modest increase in forward voltage can produce a large current increase. It also shows why the frequently quoted “0.7 V silicon drop” is not a physical constant. Forward voltage depends on current, temperature, device construction, and required accuracy.

At a specified operating point, the diode’s incremental or dynamic resistance is

r_d = dV_D/dI_D approximately equal to nV_T/I_D.

This resistance is used for small-signal analysis. It is not the same as the dc ratio V_D/I_D and should not be used when the signal is large enough to move the operating point substantially.

Levels of Circuit Modeling

The ideal-diode model assumes zero voltage drop in the forward direction and zero current in reverse bias. It is suitable for determining conduction intervals and approximate switching action.

The constant-voltage model represents a conducting silicon diode by a fixed threshold, often selected near 0.7 V. It is useful for hand calculations involving moderate currents, but the value must be treated as an approximation.

The piecewise-linear model adds a forward resistance r_f after a threshold voltage V_gamma:

V_D = V_gamma + I_D r_f.

This model is valuable in rectifier and power calculations because it estimates both voltage loss and conduction loss.

The exponential model is required for precision bias calculations, temperature studies, low-level signal analysis, and device comparison. For a circuit with several nonlinear diodes, the operating point can be found by combining the diode equation with Kirchhoff’s laws, often using graphical methods or Newton–Raphson iteration.

For an ac signal superimposed on a dc bias, the small-signal model replaces the diode by r_d, together with junction capacitance where necessary. The total small-signal admittance may include diffusion capacitance in forward bias and depletion capacitance in reverse bias.

Temperature and High-Frequency Effects

Temperature affects both the saturation current and the forward voltage. Since I_S generally increases strongly with temperature, a diode carrying a fixed current requires a lower forward voltage as temperature rises. A commonly used engineering approximation for silicon diode forward-voltage change is about −2 mV/°C, although the exact value depends on current and device technology. This negative coefficient can cause current hogging when several diodes or transistor junctions are connected in parallel without ballast resistance.

Reverse leakage also increases with temperature. In precision rectifiers, sample-and-hold circuits, and battery-powered equipment, leakage can dominate the intended signal.

A reverse-biased junction behaves partly as a capacitor. Its depletion capacitance decreases as reverse voltage increases. Under forward bias, stored minority charge produces diffusion capacitance and delays turn-off. In a switching diode, the reverse-recovery interval can create substantial current spikes and switching loss. Fast-recovery, Schottky, and specialized soft-recovery diodes are selected when high-frequency performance matters.

Rectification: Converting Alternating Voltage to Unidirectional Voltage

A rectifier converts an alternating input into a pulsating unidirectional output. The simplest circuit is the half-wave rectifier, in which one diode conducts during one half-cycle and blocks during the other. For an ideal sinusoidal input v_s = V_m sin omega t, the average output is

V_DC = V_m/pi.

The rms output of the half-wave waveform is V_m/2, and the ripple frequency equals the input frequency. Its main disadvantages are poor transformer utilization, high ripple, and a discontinuous input current.

A full-wave rectifier uses both half-cycles. A center-tapped circuit requires a transformer with a center tap and two diodes. A bridge rectifier uses four diodes and does not require a center-tapped transformer. In each half-cycle, two bridge diodes conduct, so the approximate output peak is V_m − 2V_D. For an ideal full-wave rectifier,

V_DC = 2V_m/pi,

and ripple occurs at twice the supply frequency. The bridge is usually preferred because transformer utilization is better and the secondary winding is simpler, although its two-diode conduction path increases voltage loss.

Capacitor-Input Filtering

Connecting a capacitor across the rectifier output allows the capacitor to charge near the peak of the waveform and supply the load while the rectifier voltage falls below the capacitor voltage. For a full-wave rectifier, the approximate ripple peak-to-peak voltage is

V_r(pp) approximately I_L/(2fC),

where f is the input frequency, I_L is load current, and C is filter capacitance. The dc output is approximately

V_DC approximately V_peak − V_r(pp)/2 − diode losses.

The diodes conduct only for short intervals near each input peak. Consequently, the source current has high peaks and a poor power factor. A larger capacitor reduces ripple but increases inrush current, diode peak current, transformer stress, and electromagnetic interference. A design must therefore consider more than the ripple formula.

The peak inverse voltage (PIV) is the maximum reverse voltage a diode must withstand. In a center-tapped full-wave rectifier, the PIV requirement can be approximately twice the peak voltage of one half-secondary. In a bridge, each nonconducting diode commonly experiences approximately the secondary peak voltage, subject to circuit details and transients.

Other Filter and Regulation Choices

An RC filter reduces ripple effectively at low current but wastes voltage and power in the series resistor. An LC filter provides better performance at higher power but is larger and may exhibit resonance. A regulated supply adds a control element that maintains output voltage against input and load variations. The appropriate architecture may be an unregulated rectifier, a linear regulator, a switching regulator, or a hybrid arrangement.

Waveform-Shaping Circuits

Clippers

A clipper limits a waveform above or below a selected level. In a series clipper, the diode is placed in series with the signal path; in a shunt clipper, it diverts signal current when a threshold is reached. A biased clipper uses a dc source to establish a clipping level other than zero. With a real diode, the clipping threshold includes the diode forward voltage and source polarity.

For example, a positive shunt clipper designed with a reference V_R conducts when the input attempts to exceed approximately V_R + V_D. The output is then held near that level, although its exact value depends on diode dynamic resistance and the current-limiting resistor. A resistor is essential because it limits current during the conducting interval.

Clippers protect instrument inputs, shape communication waveforms, and remove unwanted portions of sensor signals. Their design must account for diode power, transition speed, and the effect of source and load resistance.

Clampers

A clamper shifts the dc level of an ac waveform while ideally preserving its peak-to-peak amplitude. It contains a diode, capacitor, and resistor. During one half-cycle the diode conducts and rapidly charges the capacitor; during the other half-cycle the diode is off and the capacitor voltage adds to or subtracts from the input.

For effective clamping, the charging time constant during conduction should be small, while the discharge time constant R_L C should be large compared with the signal period. If R_L C is too small, the capacitor discharges significantly and the waveform develops tilt. A practical clamper also suffers from diode drop, leakage, source resistance, and finite charging time. Clampers are used in dc restoration, television and imaging circuits, level shifting, and protection interfaces.

Peak Detectors and Envelope Detectors

A peak detector is a rectifier followed by a capacitor. The capacitor charges when the input exceeds its stored voltage plus the diode drop and discharges through the load when the input falls. It can measure signal peaks, generate control voltages, or recover the envelope of an amplitude-modulated signal.

For envelope detection, the discharge time constant must be much longer than the carrier period but short enough to follow the modulation envelope. If the time constant is too short, excessive ripple appears; if too long, diagonal clipping occurs because the detector cannot follow rapid envelope decreases. A precision rectifier using an operational amplifier can reduce the effect of diode forward drop for small signals, but amplifier bandwidth, slew rate, input offset, and overload recovery then become relevant.

Voltage Multipliers

Voltage multipliers use capacitors and diodes to obtain a dc voltage greater than the peak of an ac source without a high-ratio transformer. In a doubler, one capacitor charges on one half-cycle and another is stacked in series with the source on the next half-cycle. Ideal no-load output can approach 2V_m. Voltage tripler and higher-order multiplier structures extend this principle.

The advantages are simplicity and high voltage at low current. The disadvantages include poor regulation, ripple, capacitor voltage stress, diode reverse stress, and slow startup. Under load, the output falls because charge must be replenished through finite conduction intervals. A rough design must evaluate load current, operating frequency, capacitance, allowable ripple, and the voltage ratings of every capacitor and diode. Multipliers are common in low-current high-voltage bias supplies, displays, and scientific instruments, but are generally unsuitable for high-power regulation.

Zener Diodes and Shunt Regulation

A Zener diode is designed to operate in reverse breakdown at a specified voltage. Breakdown may be dominated by the Zener effect at lower voltages or avalanche multiplication at higher voltages; practical devices may involve both mechanisms. The breakdown voltage has a temperature coefficient that can be negative, positive, or near zero depending on the operating voltage and construction.

A basic shunt regulator consists of a series resistor R_S, a Zener diode connected in reverse bias across the load, and the load itself. If the supply is V_S and the regulated voltage is approximately V_Z,

I_S = (V_S − V_Z)/R_S,

and

I_S = I_L + I_Z.

Regulation is maintained only if the Zener current remains between its minimum knee current I_ZK and its maximum permissible current, commonly determined from rated power P_Z(max):

I_Z(max) = P_Z(max)/V_Z.

The resistor must be chosen to satisfy worst-case conditions. At minimum input and maximum load, the Zener must still have sufficient current. At maximum input and minimum load, its current and power must remain safe. The design inequalities are

(V_S(min) − V_Z)/R_S ≥ I_L(max) + I_Z(min)

and

(V_S(max) − V_Z)/R_S ≤ I_L(min) + I_Z(max).

If no resistor satisfies both inequalities, the shunt regulator is unsuitable for the specified range. A series-pass or switching regulator should then be considered.

The dynamic resistance r_Z = dV_Z/dI_Z determines small-signal regulation. A lower dynamic resistance gives better line and load regulation. A bypass capacitor may improve ac noise performance, while a fuse or current limiter protects against sustained faults.

Applied Design Example: A Low-Current Regulated Supply

Consider an illustrative design requiring approximately 9.1 V across a load that varies from 5 mA to 20 mA. The rectifier and transformer provide an input varying from 14 V to 18 V dc. Select a Zener minimum operating current of 5 mA and a maximum allowable Zener current of 40 mA.

At minimum input and maximum load, the series resistor must satisfy

R_S ≤ (14 − 9.1)/(20 mA + 5 mA) = 196 ohms.

At maximum input and minimum load, it must satisfy

R_S ≥ (18 − 9.1)/(5 mA + 40 mA) = 198 ohms.

The narrow and slightly inconsistent interval indicates that the nominal requirements leave little design margin. Component tolerances, Zener-voltage variation, rectifier ripple, and temperature could easily violate regulation. The designer should either reduce the load range, increase the available input headroom, select a different Zener current range, or use an active regulator. This example illustrates an important professional principle: an algebraically valid nominal design may still be a poor production design if tolerances and extremes are ignored.

Detailed Illustrative Case Study: Input Protection for a Data-Acquisition Module

Background

A laboratory data-acquisition module accepts a sensor signal nominally between −2 V and +2 V. Its analog-to-digital converter has an absolute maximum input range of −0.3 V to 3.6 V. The module may be connected to sensors with long cables, where electrostatic discharge and wiring faults are possible.

Problem

A protection network must prevent destructive overvoltage while adding minimal leakage and capacitance during normal measurement. A simple pair of ordinary rectifier diodes is considered first.

Analysis

The protection current during an overvoltage event must be limited. If the input is accidentally driven to 12 V and the upper clamp is approximately 3.6 V, a series resistor is needed to restrict current. However, the resistor and input capacitance form a low-pass network that may reduce measurement bandwidth. Ordinary power diodes have relatively high leakage and junction capacitance, whereas small-signal or Schottky diodes may offer lower forward drop but can have significant reverse leakage. The ADC’s internal protection diodes must not be assumed to carry continuous fault current.

Approach and Solution

The design uses a series resistor selected from the maximum permissible clamp current and the required signal bandwidth. Low-leakage external diodes connect to precision reference rails, with local decoupling capacitors. A separate transient suppressor is placed at the connector, where it absorbs high-energy events before they reach the precision clamp. The protection network is verified for positive and negative faults, power dissipation, startup conditions, and the possibility that the reference rail itself is unpowered.

Outcome

The resulting two-stage network separates high-energy transient suppression from low-leakage signal clamping. It protects the converter without relying on an untested assumption about internal diode ratings. The final design is validated by injection-current testing, oscilloscope measurements, temperature testing, and fault-condition analysis.

Learning Points

The case demonstrates that diode selection is a system decision. Forward voltage alone is insufficient; leakage, capacitance, surge rating, thermal path, fault energy, reference-rail behavior, and measurement accuracy must also be considered. Protection components should be tested under realistic fault waveforms rather than only under steady dc conditions.

Limitations, Failure Modes, and Professional Practice

Common mistakes include treating the 0.7 V drop as universal, neglecting the second diode drop in a bridge, confusing PIV with forward-current rating, omitting current limiting in a clipper or Zener circuit, and calculating ripple without checking capacitor ripple current or inrush current. Another frequent error is using the ideal-diode model in a low-level detector, where the forward drop is comparable to the signal.

Thermal design is essential. Diode power is approximately P_D = V_D I_D in forward conduction and V_Z I_Z in Zener operation. The junction temperature follows T_J = T_A + P_D theta_JA for a simple thermal-resistance model. Maximum ratings must be derated for ambient temperature, airflow, mounting, and repetitive versus nonrepetitive operation.

Safety considerations become important in high-voltage multiplier and rectifier circuits. Stored capacitor energy can remain hazardous after disconnection. Creepage, clearance, insulation, discharge resistors, fusing, and protective enclosures should be designed according to applicable standards and the intended environment. Semiconductor datasheets are authoritative for ratings, test conditions, and recommended operating limits; generic nominal values should never replace them.

Modern simulation tools can solve nonlinear diode circuits, perform parameter sweeps, estimate ripple, and reveal transient current. Automated design is useful when models include realistic parasitics and tolerances. A simulation that uses ideal diodes cannot establish compliance or reliability. Measurement remains necessary, particularly for reverse recovery, surge current, thermal behavior, conducted emissions, and breakdown operation.

Emerging diode technologies include silicon-carbide and gallium-nitride power devices, which provide high-temperature or high-frequency advantages in suitable applications. Schottky diodes offer low forward voltage and fast switching but generally exhibit higher leakage and lower reverse-voltage capability than comparable pn diodes. Integrated protection structures, active rectifiers, synchronous rectification, and precision semiconductor switching continue to reduce conduction loss, though they introduce control complexity and new failure modes.

Best-Practice Design Sequence

A robust diode-circuit design normally proceeds as follows:

1. Define input range, load range, waveform, frequency, allowable ripple, accuracy, temperature, and fault conditions.

2. Determine conduction states using an ideal model, then refine the result with voltage drop and resistance.

3. Check forward current, reverse voltage, surge current, reverse recovery, leakage, capacitance, and power dissipation.

4. Analyze worst-case combinations of component tolerance, temperature, supply variation, and load variation.

5. Select a device using datasheet curves rather than a single nominal rating.

6. Verify thermal margins, layout, insulation, electromagnetic compatibility, and service safety.

7. Confirm the design experimentally with normal, transient, startup, shutdown, and fault tests.

Chapter Summary

A p–n junction results from the balance between carrier diffusion and the electric field of its depletion region. Forward bias reduces the junction barrier and produces an approximately exponential current, whereas reverse bias produces leakage until breakdown. The diode equation, dynamic resistance, junction capacitance, and temperature dependence provide the basis for practical modeling.

Diode circuits perform rectification, filtering, waveform clipping, dc restoration, peak detection, voltage multiplication, and voltage regulation. Half-wave, full-wave, and bridge rectifiers differ in ripple, diode stress, transformer utilization, and conduction loss. Clippers and clampers require correct polarity, current limiting, and time-constant selection. Zener regulators require simultaneous checks at minimum input/maximum load and maximum input/minimum load. Throughout the design process, non-idealities—including forward drop, leakage, reverse recovery, capacitance, thermal limits, tolerances, and breakdown behavior—must be included. Professional diode design is therefore an exercise in selecting an appropriate model, evaluating worst cases, and validating the complete system.

Key Terms

P–n junction: Interface between p-type and n-type semiconductor regions.

Depletion region: Junction region depleted of mobile carriers and containing fixed ionized dopants.

Built-in potential: Equilibrium potential barrier established by carrier diffusion and the junction electric field.

Forward bias: Bias that reduces the junction barrier and promotes substantial current conduction.

Reverse bias: Bias that increases the barrier and normally permits only a small leakage current.

Saturation current: Reverse-current parameter appearing in the exponential diode equation.

Ideality factor: Parameter describing departure of a practical junction from ideal exponential behavior.

Thermal voltage: Quantity kT/q, approximately 25.85 mV at room temperature.

Dynamic resistance: Incremental voltage-to-current ratio at a specified operating point.

PIV: Maximum repetitive reverse voltage a rectifier diode must withstand.

Reverse recovery: Turn-off interval required for a conducting diode to cease carrying significant reverse current.

Clipper: Diode network that limits a waveform to a selected voltage range.

Clamper: Diode-capacitor network that shifts waveform dc level.

Peak detector: Rectifier-capacitor circuit that stores an input peak or envelope.

Voltage multiplier: Diode-capacitor circuit that produces dc voltage greater than the source peak.

Zener breakdown: Controlled reverse-breakdown operation used for voltage reference or regulation.

Dynamic Zener resistance: Small-signal slope dV_Z/dI_Z in the breakdown region.

Ripple: Residual periodic ac variation on a rectifier’s dc output.

Junction capacitance: Voltage-dependent capacitance associated with a reverse-biased depletion region.

Thermal resistance: Parameter relating device power dissipation to junction temperature rise.

Review Questions

Short Answer Questions

1. Why does a depletion region form when p-type and n-type materials are joined?

2. Define thermal voltage and state its approximate value at room temperature.

3. Distinguish PIV from the forward-current rating of a rectifier diode.

4. What is the purpose of a series resistor in a Zener shunt regulator?

5. Why must a clamper have a large discharge time constant relative to the signal period?

Long Answer Questions

1. Derive the qualitative current–voltage behavior of a p–n junction and explain the role of the ideality factor.

2. Compare half-wave, center-tapped full-wave, and bridge rectifiers in terms of output, diode stress, transformer utilization, and ripple.

3. Explain capacitor-input filtering and derive the approximate full-wave ripple relation.

4. Describe the operation and design constraints of clippers, clampers, and peak detectors.

5. Explain Zener breakdown and develop the worst-case design inequalities for a shunt regulator.

Analytical / Application Questions

1. A bridge rectifier supplies a capacitor-input load. Explain how increasing capacitance affects ripple, conduction angle, inrush current, and diode stress.

2. A Zener regulator loses regulation at high load current but overheats at light load. Identify the governing inequalities and propose design changes.

3. A peak detector produces severe ripple on a modulated signal. Determine whether the time constant is too small or too large, and explain the resulting waveform distortion.

22. Multiple Choice Questions with Answers

Question 1

Which physical mechanism primarily establishes the electric field in the depletion region of an equilibrium p–n junction?

A. Uniform motion of externally supplied electrons

B. Fixed ionized donor and acceptor charges left after carrier diffusion

C. Avalanche multiplication throughout the neutral regions

D. Thermal expansion of the semiconductor lattice

Correct Answer: B. Fixed ionized donor and acceptor charges left after carrier diffusion

Question 2

For a diode carrying a forward current I_D under diffusion-dominated operation, its approximate small-signal resistance is

A. I_D/(nV_T)

B. nV_T I_D

C. nV_T/I_D

D. V_D/I_D only, independent of temperature

Correct Answer: C. nV_T/I_D

Question 3

In an ideal full-wave bridge rectifier connected to a sinusoidal source of peak V_m, the average output voltage is

A. V_m/(2pi)

B. V_m/pi

C. 2V_m/pi

D. pi V_m/2

Correct Answer: C. 2V_m/pi

Question 4

What is the principal consequence of placing a large capacitor directly across a rectifier output?

A. The diode never conducts

B. Ripple decreases, but charging-current peaks generally increase

C. The ripple frequency becomes half the supply frequency

D. The output becomes exactly equal to the source rms voltage

Correct Answer: B. Ripple decreases, but charging-current peaks generally increase

Question 5

A clipper resistor is primarily required to

A. Increase the diode reverse saturation current

B. Limit current when the diode conducts

C. Eliminate junction capacitance

D. Make the diode ideal at all frequencies

Correct Answer: B. Limit current when the diode conducts

Question 6

For effective operation of a clamper, the load-capacitor discharge time constant should generally be

A. Much smaller than the signal period

B. Approximately zero

C. Much larger than the signal period

D. Independent of signal frequency

Correct Answer: C. Much larger than the signal period

Question 7

A Zener shunt regulator is most likely to lose regulation when

A. The Zener current falls below its knee current

B. The resistor has a nonzero value

C. The load is disconnected and Zener current rises

D. The input voltage is within its specified range

Correct Answer: A. The Zener current falls below its knee current

Question 8

Which condition is most directly associated with reverse-recovery loss in a switching diode?

A. Stored minority charge must be removed after forward conduction

B. The diode has zero junction capacitance

C. The diode is permanently open-circuit

D. The input waveform has no transitions

Correct Answer: A. Stored minority charge must be removed after forward conduction

Question 9

In a Zener regulator, the worst case for ensuring sufficient Zener current is generally

A. Maximum input voltage and minimum load current

B. Minimum input voltage and maximum load current

C. Maximum input voltage and maximum load current only

D. Minimum input voltage and minimum load current only

Correct Answer: B. Minimum input voltage and maximum load current

Question 10

A protection diode network for a data-acquisition input must be evaluated not only for forward voltage but also for

A. Leakage, capacitance, fault current, and reference-rail behavior

B. Color of the package exclusively

C. The ideal-diode assumption only

D. The nominal input voltage without transients

Correct Answer: A. Leakage, capacitance, fault current, and reference-rail behavior